This invention relates to an improved elevator assembly adapted for use with a well drilling apparatus in order to lift or lower drilling tubulars quickly and efficiently.
In a wide variety of well drilling operations, it is necessary to assemble a drill string from a large number of individual lengths of drill pipe as a borehole is being drilled. When it becomes necessary for any reason to remove the drill string from borehole, as for example to replace worn drill bit, the drill string must be progressively raised as successive lengths of drill pipe are brought to the surface and removed from the drill string. Well servicing requires similar equipment, which, in smaller sizing, is used to pull or replace sucker rods, production piping, etc., for pump service, replacement of worn pipes or rods, or during well cleanout to improve production.
One type of drilling apparatus in wide-spread use utilizes a power swivel which is threadedly coupled to the uppermost length of drill pipe and then used to raise the drill string and to remove the uppermost length of drill pipe from the string. Once this has been accomplished, the threaded connection between the power swivel and the uppermost length of drill pipe is broken, and means such as a transfer arm can then be used to move the length of drill pipe from the vertical position aligned with the borehole to a horizontal position at ground level.
This prior art approach to raising a drill string and successively removing lengths of drill pipe from the string is not entirely acceptable. It requires that the power swivel be threadedly coupled to each successive length of drill pipe, and that this threaded connection then be broken. These repeated threading and unthreading operations can significantly slow the rate at which drill pipe can be removed from a borehole. In addition, these threading and unthreading operations can cause undesirable wear on the threaded connections of the swivel and of the drill pipe.
It is therefore an object of this invention to provide an improved apparatus useful in removing drill pipe from a borehole, and in particular to provide such an apparatus which does not require threaded connections between the apparatus and the drill pipe, and which can be used to speed the rate at which drill pipe can be removed from a borehole.
An additional object of this invention is to provide an improved apparatus as compared to the invention of U.S. patent application Ser. No. 430,943, using linkages to control the movement of the jaws, rather than a collar.
A further object of the present invention is to provide a mechanism for locking the jaws open to receive or release a length of pipe, or to allow changing jaw inserts to accommodate different sizes of pipe, and for unlocking the jaws to allow closure over and clamping of a length of pipe.